We began with a baseline 111_111 model containing one common genetic, one common shared environmental and one common unique environmental factor as well as criterion-specific genetic, shared environmental and unique environmental factors (model 1 in Table 2). The results for all other models in Table 2 (Δχ2, Δdf and Δ AIC) were calculated relative to model 1. In this baseline model, thresholds were allowed to differ between the sexes, but no quantitative or qualitative sex effects were present. Models 2 and 3 introduced, respectively, quantitative and qualitative sex effects. Compared with model 1, the AIC of model 2 deteriorated but that of model 3 was improved. Therefore, all subsequent model fitting included both qualitative sex effects and thresholds that differed between men and women. In models 4, 5 and 6 we set, respectively, all shared environmental, genetic and both genetic and shared environmental criterion-specific effects to zero. Model 6 clearly fits best by AIC, indicating that no criteria-specific genetic or familial environmental effects were needed in this model.
